Class delegation with by keyword in Kotlin - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to delegate the interface implementation using the 'by' keyword.

Kotlin

interface Printer {
    fun printMessage()
}

class ConsolePrinter : Printer {
    override fun printMessage() {
        println("Printing to console")
    }
}

class Delegator(private val printer: Printer) : Printer [1] printer

fun main() {
    val printer = ConsolePrinter()
    val delegator = Delegator(printer)
    delegator.printMessage()
}

Drag options to blanks, or click blank then click option'

Aimplements

Bextends

Cby

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'implements' or 'extends' which are Java keywords, not Kotlin delegation keywords.

Using ':' alone without 'by' does not delegate implementation.

In Kotlin, the 'by' keyword is used for class delegation to delegate interface implementation to another object.

2fill in blank

medium

Complete the code to delegate the 'calculate' function to the CalculatorImpl class.

Kotlin

interface Calculator {
    fun calculate(x: Int, y: Int): Int
}

class CalculatorImpl : Calculator {
    override fun calculate(x: Int, y: Int): Int {
        return x + y
    }
}

class DelegatedCalculator(private val calc: Calculator) : Calculator [1] calc

fun main() {
    val calculator = CalculatorImpl()
    val delegated = DelegatedCalculator(calculator)
    println(delegated.calculate(5, 3))
}

Drag options to blanks, or click blank then click option'

Aimplements

Bby

Cextends

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using Java keywords like 'implements' or 'extends' instead of Kotlin's 'by'.

Omitting the delegation keyword causes a compilation error.

The 'by' keyword delegates the interface implementation to the provided object in Kotlin.

3fill in blank

hard

Fix the error in the delegation syntax to correctly delegate the 'speak' function.

Kotlin

interface Speaker {
    fun speak()
}

class EnglishSpeaker : Speaker {
    override fun speak() {
        println("Hello")
    }
}

class Person(private val speaker: Speaker) : Speaker [1] speaker

fun main() {
    val englishSpeaker = EnglishSpeaker()
    val person = Person(englishSpeaker)
    person.speak()
}

Drag options to blanks, or click blank then click option'

Aby

Bimplements

Cextends

D:

Attempts:

3 left

💡 Hint

Common Mistakes

Using Java keywords like 'implements' or 'extends' instead of 'by'.

Using ':' alone without 'by' causes syntax errors.

The correct Kotlin syntax for delegation uses the 'by' keyword to delegate interface implementation.

4fill in blank

hard

Fill both blanks to delegate the 'draw' function to the 'ShapeImpl' class.

Kotlin

interface Shape {
    fun draw()
}

class ShapeImpl : Shape {
    override fun draw() {
        println("Drawing shape")
    }
}

class ShapeDelegate(private val shape: Shape) : Shape [1] [2]

fun main() {
    val shapeImpl = ShapeImpl()
    val shapeDelegate = ShapeDelegate(shapeImpl)
    shapeDelegate.draw()
}

Drag options to blanks, or click blank then click option'

Aby

Bimplements

Cshape

Dextends

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'implements' or 'extends' instead of 'by'.

Not specifying the object to delegate to.

The 'by' keyword delegates the interface implementation to the object 'shape'.

5fill in blank

hard

Fill all three blanks to delegate the 'play' function to the 'MusicPlayerImpl' class and override it in the delegator.

Kotlin

interface MusicPlayer {
    fun play()
}

class MusicPlayerImpl : MusicPlayer {
    override fun play() {
        println("Playing music")
    }
}

class CustomPlayer(private val player: MusicPlayer) : MusicPlayer [1] [2] {
    override fun play() {
        println("Custom player start")
        player.[3]()
        println("Custom player end")
    }
}

fun main() {
    val impl = MusicPlayerImpl()
    val custom = CustomPlayer(impl)
    custom.play()
}

Drag options to blanks, or click blank then click option'

Aby

Bplayer

Cplay

Dimplements

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'implements' instead of 'by'.

Forgetting to call the delegated function inside the override.

Using wrong variable or function names.

Use 'by' to delegate, 'player' as the delegate object, and call 'play()' on it inside the override.